1. Field of the Invention
This invention relates to a light source unit including a linear light source portion with plural glass-sealed LEDs (light emitting diodes) mounted thereon, and a heat radiation portion connected to the linear light source portion.
2. Description of the Related Art
A linear light source unit is known in which plural LED elements are mounted on an elongate wiring board and the LED elements are sealed with a resin sealing material on the wiring board (See, e.g., JP-A-2006-344450, paragraph [0005]). However, this linear light source unit has the problems that, due to heat generated from the LED elements, the resin sealing material is yellowed by deterioration to cause an reduction in light intensity with time, or the resin sealing material is separated from the wiring board to cause a contact failure.
In order to solve the problems, JP-A-2006-344450 discloses a linear light source unit that is composed of plural LED elements arranged on the wiring board, and a glass material formed on the wiring board for covering the LED elements (e.g., paragraph [0021]). JP-A-2006-344450 states that the glass material has thermal conductivity about five times higher than the conventional resin material and, therefore, amount of heat dissipated outside from the LED elements increases to suppress temperature rise of the LED elements.
However, since the thermal conductivity of the glass material and the resin material is much lower than that of a metal material etc., the heat radiation property of the sealing material of the linear light source unit of JP-A-2006-344450 is still insufficient though the glass material has thermal conductivity higher than the conventional resin material. In other words, the linear light source unit of JP-A-2006-344450 does not provide enough improvement in heat radiation property as compared to that the conventional linear light source unit with the resin sealing material, and the amount of heat from the LED elements acceptable in the entire unit is equal to the conventional linear light source unit with the resin sealing material. Thus, although the linear light source unit of JP-A-2006-344450 allows an increase in amount of heat from the LED elements by using the glass sealing material, thermal load is eventually applied to each LED element since the entire unit is problematic in the heat radiation property of the LED elements. Therefore, it is infeasible to improve the performance of the light source unit by increasing the light intensity of the LED elements or by densely arranging the LED elements since heat generation increases thereby. As a result, the performance of the LED elements cannot be sufficiently utilized.